Wafer level packaging (WLP) technology combines dies having different functionalities at a wafer level, and is widely applied in order to meet continuous demands toward the miniaturization and higher functions of electronic components. The WLP technology includes few operations, such as bonding two different wafers into an integral part (called wafer bonding hereinafter) and then proceeding to a sigulation process to cut the integral part into a singulated package.
Fusion bonds and hybrid bonds are two terms generally used to categorize various wafer bonding methods. A fusion bond refers to a wafer bonding method in which there is only dielectric material involved on the bonding surface. The hybrid bond, on the other hand, refers a wafer bonding method in which has a dielectric and a metallic material contained on the bonding surface. The hybrid bond is more complicated than the fusion bond because it includes two different materials. In some examples such as CMOS image sensor (CIS) wafer bonding, a bonded interface includes copper and silicon oxide.
The wafer bonding is based on chemical bonds between two surfaces of any materials that meet numerous requirements specified for the wafer surface. As such, the wafer surface must be clean. Otherwise, unbonded areas called voids, i.e. interface bubbles, can occur. However, during a wafer bonding process, cleanness of a wafer surface is a challenge and affected by some factors, such as cross contamination or clean tool deviation. Thus, a system or a method to provide a clean wafer surface is still in great demand.